The present invention relates to surgical cables, particularly cerclage cables that are used in surgical procedures to stabilize fractures and to secure various types of prosthesis to bones.
Cerclage fixation by wires, sutures and cables has been used for some time to repair fractured bones and to secure prosthetic devices to bones, particularly in the spine. Originally, surgical fixation was achieved by stiff stainless steel wires which could be molded into shape and passed around or between various bones and then twisted together to tighten the wire around the bone or around the prosthesis. The use of surgical cable or wire devices of this type for this purpose is disclosed in the following Stephens, et.al. U.S. Pat. No. 4,604,995; Dove, et.al. U.S. Pat. No. 4,686,970 Steffee, U.S. Pat. No. 4,790,303 and Mehdian U.S. Pat. No. 5,092,868.
The wire used to repair fractured bones or to secure the prosthesis to bone have generally been monofilament stainless steel or titanium. These materials had sufficient malleability to enable the physician or operating room personnel to shape the wire into the desired configuration to pass the wire between or around bones. An example of this technique is shown in the above mentioned U.S. Pat. No. 5,092,868.
The problem with wires of this type is that they were extremely hard and stiff, and for that reason great care had to be exercised in the operating room in moving the wire around bones since it could cause serious or irreparable damage to the underlying soft tissue if the tissue was inadvertently contacted with excessive force. This is particularly true in the spinal column in procedures in which a prosthesis or a bone graft is affixed to the vertebrae to stabilize the vertebrae.
More recently, there has become available a relatively soft and flexible cable which avoids the problem of the stiff wires previously used. These new soft flexible cables have comparable strength to the stiff cables previously used. They are made with multiple wire filaments fully work hardened and twisted together to form a strand and then a plurality of these strands are twisted together around a core strand to make a strong flexible cable. These cables are a marked improvement over the wire which have previously been used. However, because of the flexibility and relatively little ductility they are difficult to form and pass around bone segments in the vertebrae or around bones that are not readily accessible.